Each day a different image or photograph is featured, with an
accompanying caption, which deals with various topics in Earth Science.

Vivid Sun Dog Pair

The impressive photo above showing a pair of matching sun dogs or parhelia was taken from Carleton Place, Ontario, Canada on December 23, 2004. Facing southeast, this intense display lasted roughly 15 minutes. The temperature on this bitter cold morning was -35ºC (-31 F). Ice crystals typically found in cirrus clouds give rise to halo phenomena, but they may also result in blowing and drifting snow just a few meters above the surface. Sun dogs are created when sunlight passes through hexagonal, pencil-shaped ice crystals that are horizontally aligned. They form 22 degrees on either side of the Sun or Moon at a maximum angle of 45º above the horizon -- they're not seen high in the sky. Usually they appear as one or two luminous spots, looking like false Suns, and in many cases one dog is brighter than the other. Periodically, they can be seen tinted with red on the inside and blue on the outside, as seen here. Note the faint parhelic circle -- the colorless arc of light extending through the Sun and parhelia. Under ideal conditions, it can be observed circling the entire sky at the Sun's altitude.